Head First设计模式-简单工厂模式

开始之前，先讲下java直接new一个对象

Pizza  pizza = new CheesePizza(); ;

对象pizza使用了接口，是代码更具有弹性，但是CheesePizza还是建立了具体的类，当有一群具体的类，如：

1.                 Pizza pizza = null;  
2.   
3.                 if (type.equals("cheese")) {  
4.                         pizza = new CheesePizza();  
5.                 } else if (type.equals("pepperoni")) {  
6.                         pizza = new PepperoniPizza();  
7.                 }  

面向接口编程

面向接口编程，可以隔离掉以后系统可能发生的改变。如果代码使用具体的类，就要修改代码。也就是非“对修改关闭”。当要扩展时，就必须打开它。所以要回到OO设计原则，找到变化的方面，把它们从不变的部分分离出来。

一、简单工厂模式

       PizzaStore.java

public class PizzaStore {          SimplePizzaFactory factory;//多用组合，少用继承            public PizzaStore(SimplePizzaFactory factory) {                  this.factory = factory;          }            public Pizza orderPizza(String type) {                  Pizza pizza;                    pizza = factory.createPizza(type);                    pizza.prepare();                  pizza.bake();//面向接口编程                  pizza.cut();                  pizza.box();                    return pizza;          }    }  

SimplePizzaFactory.java

public class SimplePizzaFactory {            public Pizza createPizza(String type) {                  Pizza pizza = null;                    if (type.equals("cheese")) {                          pizza = new CheesePizza();                  } else if (type.equals("pepperoni")) {                          pizza = new PepperoniPizza();                  }                  return pizza;          }  } 

Pizza.java

import java.util.ArrayList;    abstract public class Pizza {      String name;      String dough;      String sauce;      ArrayList toppings = new ArrayList();        public String getName() {          return name;      }        public void prepare() {          System.out.println("Preparing " + name);      }        public void bake() {          System.out.println("Baking " + name);      }        public void cut() {          System.out.println("Cutting " + name);      }        public void box() {          System.out.println("Boxing " + name);      }        public String toString() {          // code to display pizza name and ingredients          StringBuffer display = new StringBuffer();          display.append("---- " + name + " ----\n");          display.append(dough + "\n");          display.append(sauce + "\n");          for (int i = 0; i < toppings.size(); i++) {              display.append((String )toppings.get(i) + "\n");          }          return display.toString();      }  }

         CheesePizza.java 

[java] view plaincopy

1. public class CheesePizza extends Pizza {  
2.         public CheesePizza() {  
3.                 name = "Cheese Pizza";  
4.                 dough = "Regular Crust";  
5.                 sauce = "Marinara Pizza Sauce";  
6.                 toppings.add("Fresh Mozzarella");  
7.                 toppings.add("Parmesan");  
8.         }  
9. }  

        PepperoniPizza.java

[java] view plaincopy

1. public class PepperoniPizza extends Pizza {  
2.         public PepperoniPizza() {  
3.                 name = "Pepperoni Pizza";  
4.                 dough = "Crust";  
5.                 sauce = "Marinara sauce";  
6.                 toppings.add("Sliced Pepperoni");  
7.                 toppings.add("Sliced Onion");  
8.                 toppings.add("Grated parmesan cheese");  
9.         }  
10. }  

          PizzaTestDrive.java

[java] view plaincopy

1. public class PizzaTestDrive {  
2.   
3.         public static void main(String[] args) {  
4.                 SimplePizzaFactory factory = new SimplePizzaFactory();  
5.                 PizzaStore store = new PizzaStore(factory);  
6.   
7.                 Pizza pizza = store.orderPizza("cheese");  
8.                 System.out.println("We ordered a " + pizza.getName() + "\n");  
9.   
10.                 pizza = store.orderPizza("pepperoni");  
11.                 System.out.println("We ordered a " + pizza.getName() + "\n");  
12.         }  
13. }  

二、结果如下：

 三、原来creatPizza的位置代码如下：

[java] view plaincopy

1. if (type.equals("cheese")) {  
2.                        pizza = new CheesePizza();  
3.                } else if (type.equals("pepperoni")) {  
4.                        pizza = new PepperoniPizza();  
5.                } else if (type.equals("clam")) {  
6.                        pizza = new ClamPizza();  
7.                } else if (type.equals("veggie")) {  
8.                        pizza = new VeggiePizza();  
9.                }  
10.                return pizza;  

     因为此部分是变化的，简单工厂模式封装了变化。实现了松耦合。